JPH07321052A - Method of manufacturing polycrystalline semiconductor film - Google Patents

Abstract

PURPOSE:To provide the method of manufacturing a polycrystalline semiconductor film with expanded crystalline particle diameter. CONSTITUTION:A semiconductor film 3 to be a starting material formed on a substrate 1 as a sample 5 is fixed in a substrate holder 6 comprising a piezoelectric oscillating element 7. Next, the piezoelectric element 7 is impressed with a voltage to generate ultrasonic oscillation as well as laser-anneal for molten recrystallization of the semiconductor film 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polycrystalline semiconductor film.

[0002]

2. Description of the Related Art A thin film transistor (TFT) is used, for example, in a drive device of an active matrix type liquid crystal panel. When forming this thin film transistor, a polycrystalline semiconductor film such as a p-type or n-type doped polycrystalline Si film is used as the material. In order to obtain a higher field effect mobility in a thin film transistor, it is better that the number of crystal grain boundaries that act as a barrier for electrons is smaller, and therefore the larger the crystal grain size of the polycrystalline semiconductor film is.

Therefore, various methods have been proposed to increase the crystal grain size of the polycrystalline semiconductor film. Method 1
H. Kuriyama et al .: Japanese Journal of A
pplied Physics, Vol. 30, No. 12B, December, 1991, p
There is a laser annealing method proposed on p.3700-3703. In this laser annealing method, for example, an amorphous Si film (hereinafter referred to as an a-Si film) formed by a plasma CVD method is irradiated with a laser beam in a pulsed manner, the a-Si film is once melted, and then the a-Si film is melted again. It is solidified to form a polycrystalline Si film. The physical mechanism of this method is a-Si.
It is considered that small crystal grains are formed during the process of melting and recrystallization of the film, and energy is applied to the crystal grain boundaries to destroy the crystal grain boundaries and expand the crystal grain size. ing.

[0004]

In the above laser annealing method, it is necessary to apply more energy in order to increase the crystal grain size. Therefore, when the laser output is increased or the number of laser light pulses to be applied is increased, there is a problem that film roughness occurs. Therefore, conventionally, the crystal grain size of the polycrystalline Si film is saturated to some extent.

Therefore, an object of the present invention is to provide a method for producing a polycrystalline semiconductor film which can increase the crystal grain size without causing problems such as film roughness.

[0006]

A method for producing a polycrystalline semiconductor film according to the present invention is a method for producing a polycrystalline semiconductor film using a semiconductor film on a substrate as a starting material, wherein ultrasonic waves are applied to the substrate or the semiconductor film. While the semiconductor film on the substrate is heated and melted while being recrystallized, a polycrystalline semiconductor film is formed.

[0007]

In the method for producing a polycrystalline semiconductor film according to the present invention, when the semiconductor film which is the starting material is heated and melted, ultrasonic waves are applied to the substrate or the semiconductor film to indirectly affect the semiconductor film. Energy is directly or directly applied. This promotes lateral crystal growth,
Formation of grain boundaries is prevented. As a result, the crystal grain size of the formed polycrystalline semiconductor film is further expanded. According to this method, since it is not necessary to increase the energy for heating, the film is not roughened.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a manufacturing process diagram showing a method for manufacturing a polycrystalline semiconductor film according to an embodiment of the present invention.

First, as shown in FIG. 1A, Si is formed on a substrate 1 made of glass or the like by, for example, a thermal CVD method.
The buffer layer 2 made of O ₂ or the like is formed to a thickness of 0.05 to 3 μm. Next, as shown in FIG. 1B, a non-doped p-type or n-type semiconductor film 3 as a starting material is formed on the buffer layer 2 by, for example, a plasma CVD method.
After being formed to a thickness of 05 to 3 μm, dehydrogenation is performed by annealing treatment. Furthermore, as shown in (c) of FIG.
A cap film 4 made of SiO ₂ or the like is formed on the semiconductor film 3 to have a thickness of 0.05 to 3 μm by, for example, a thermal CVD method. In this way, the sample 5 in which the buffer layer 2, the semiconductor film 3 and the cap film 4 are laminated on the substrate 1 is manufactured.

Next, as shown in FIG. 1D, the sample 5 is attached to the substrate holder 6 which vibrates ultrasonically. As the substrate holder 6, for example, a piezoelectric vibrating element 7 such as PZT having silver electrodes 8 deposited on both sides is used. here,
PZT is lead zirconate titanate (Pb (Zr, T
i) A general term for O ₃ ) type piezoelectric vibrating elements.

Then, as shown in FIG. 1 (e), a laser beam 9 is applied to the sample 5 in a state where a voltage is applied to the substrate holder 6 to generate ultrasonic vibration continuously or in a pulsed manner. Irradiate in pulses. As a laser for generating laser light, for example, an excimer laser having a wavelength of 1 μm or less is used, and the output of laser light is 0.1 to 1 J / cm ² .
In this way, a polycrystalline semiconductor film is formed using the semiconductor film 3 of Sample 5 as a starting material.

In this embodiment, the semiconductor film 3 as a starting material is used.
A non-doped a-Si film formed by the plasma CVD method was used as.

Table 1 shows the conditions for producing the polycrystalline semiconductor film in this embodiment.

[0015]

[Table 1]

As shown in Table 1, in this embodiment, the piezoelectric vibrating element 7 for applying ultrasonic waves has a resonance frequency of 2 MHz.
The sample 5 was directly fixed on the substrate holder 6 composed of the piezoelectric vibrating element 7 by using the PZT of No. 1 and set in a vacuum container, and the inside of the vacuum container was evacuated to about 10 ⁻⁴ Pa.

After that, a voltage was applied to the piezoelectric vibrating element 7 to generate ultrasonic vibration, and laser light was introduced through the ultraviolet light introduction window of the vacuum container to perform laser annealing. The substrate temperature at this time is 400 ° C. Also, as the laser light,
An ArF excimer laser with a wavelength of 193 nm was used and the energy density was set to 200 mJ / cm ² .

In this embodiment, as shown in FIG. 2 (a), the laser irradiation timing and the ultrasonic wave application timing were slightly shifted. As shown in FIG. 2B, the ultrasonic wave application timing may be substantially synchronized with the laser irradiation timing.

The voltage applied to the piezoelectric vibrating element 7 was changed from 0 V to 30 V to prepare samples of a plurality of types of polycrystalline Si films, and the maximum grain size of each polycrystalline Si film was taken by SEM (scanning electron microscope) photograph. More measured. FIG. 3 shows the relationship between the applied voltage to the piezoelectric vibrating element 7 and the maximum crystal grain size of the obtained polycrystalline Si film.

As is apparent from FIG. 3, the piezoelectric vibrating element 7
It can be seen that the maximum crystal grain size also increases as the applied voltage to V increases and the ultrasonic energy increases. For example, when a voltage of 30 V was applied to the piezoelectric vibrating element 7, the maximum crystal grain size was about 3 μm.

In the above-mentioned embodiment, the sample 5 is irradiated with the laser beam in a pulsed manner. However, even if the sample 5 is continuously irradiated with the laser beam, the crystal grain size is enlarged similarly to the above-mentioned example. A polycrystalline semiconductor film is obtained.

Further, in the above embodiment, the melt recrystallization is performed by the laser annealing method in a vacuum of about 10 ^-4 Pa, but in an inert gas atmosphere such as Ar or a gas atmosphere such as N _2. Alternatively, melt recrystallization may be performed by laser annealing.

FIG. 4 is a diagram showing a method of manufacturing a polycrystalline semiconductor film according to another embodiment of the present invention. In the embodiment of FIG. 4, a lamp annealing method is used for melting and recrystallization of the semiconductor film. This lamp annealing method is based on J. Fair and J. Meh.
lhaff: Proc. of International Flat Panel Display C
onference, Section A, pp. 109-113.

As shown in FIG. 4, (a) to (c) of FIG.
The sample 5 manufactured by the same method as the
It is installed on the substrate holder 6 made of. Halogen lamp,
Light emitted from a light source 10 composed of a xenon lamp or the like is applied to a sample 5 using a converging reflecting mirror 11 and a plane reflecting mirror 12. At the same time, similarly to the embodiment of FIG. 1, a voltage is applied to the piezoelectric vibrating element 7 and ultrasonic vibration is applied to the sample 5.

Table 2 shows the conditions for producing the polycrystalline semiconductor film in this example.

[0026]

[Table 2]

As shown in Table 2, in this embodiment, the light intensity of the light source 10 of the lamp annealing method is 100 mW / cm.
A halogen lamp of about ² was used. The diameter of the light focused on the sample 5 is set to about 2 mm, and the intensity of the light after focusing is 50 mm.
It was set to about 0 W / cm ² . The annealing time was about 3 seconds.

In this embodiment, as the piezoelectric vibrating element 7, a PZ having a resonance frequency of 2 MHz is used as in the embodiment of FIG.
Although T was used, a voltage was continuously applied to the piezoelectric vibrating element 7 and the sample 5 was melt-recrystallized by a lamp annealing method while continuously applying ultrasonic vibration. The energy density of the light focused on the sample 5 is 100 at maximum.
Since 0 W / cm ² is reached, a- deposited on the substrate 1
The Si film can be melted.

Similar to the embodiment shown in FIG. 1, the voltage applied to the piezoelectric vibrating element 7 was changed from 0 V to 30 V to prepare samples of a plurality of types of polycrystalline Si films. FIG. 5 shows the relationship between the applied voltage to the piezoelectric vibrating element 7 and the maximum crystal grain size of the obtained polycrystalline Si film.

As is apparent from FIG. 5, even when the melt recrystallization is performed by the lamp annealing method, the maximum crystal grain size increases as the applied voltage to the piezoelectric vibrating element 7 increases. For example, when a voltage of 30 V is applied to the piezoelectric vibrating element 7, the maximum crystal grain size is about 1.2 μm.
Became.

FIG. 6 is a diagram showing another example of the ultrasonic wave applying method. In the method of FIG. 6, a sample 5 manufactured by the same method as in FIGS. 1A to 1C is placed on the substrate holder 13, and ultrasonic waves are emitted from above the sample 5 using the antenna 14 and the like. At the same time, the sample 5 is irradiated with the laser beam 9.

By using the ultrasonic wave applying method shown in FIG. 6, a polycrystalline semiconductor film having an enlarged crystal grain size can be obtained as in the case of using the piezoelectric vibrating element 7. Further, the ultrasonic wave applying method of FIG. 6 may be applied to the embodiment of FIG.

In the above embodiment, ultrasonic waves are applied at the time of melting and recrystallization by the laser annealing method or the lamp annealing method, but other melting and recrystallization methods such as electron beam and flash lamp are used. Even if an ultrasonic wave is applied during the melt recrystallization, a polycrystalline semiconductor film having an enlarged crystal grain size can be obtained as in the above-mentioned embodiment.

As a starting material, non-doped p-type or n-type doped a-S formed by plasma CVD or LPCVD (low pressure chemical vapor deposition) method is used.
An amorphous semiconductor such as i can be used.

A polycrystalline semiconductor film having a relatively small crystal grain size may be used as a starting material. For example, non-doped or p-type or n-type doped polycrystalline Si formed by a solid phase growth (SPC) method or the like as a pretreatment.
A polycrystalline semiconductor film such as a film may be used as a starting material. Also in this case, a polycrystalline semiconductor film having an enlarged crystal grain size can be obtained.

Further, a non-doped or p-type or n-type doped polycrystalline Si film formed by laser annealing as a pretreatment may be used as a starting material. For example, H. Kuriyama et al .: Japanese Journal of A above.
pplied Physics, Vol. 30, No.12B, December, 1991, p
As shown in p. 3700-3703, heating the substrate at a low temperature of 500 ° C or lower to melt the a-Si film, and irradiating laser light with multiple pulses while controlling the solidification process of the melted Si. Due to the relatively small crystal grain size of polycrystalline Si
A film may be formed and the polycrystalline Si film may be used as a starting material.

A non-doped or p-type or n-type doped amorphous semiconductor film containing microcrystalline Si formed by plasma CVD or the like may be used as a starting material.

Although a sound wave having a frequency of 20 kHz or more is generally called an ultrasonic wave, in the present invention, it is 0.1 to 100 M from the viewpoint of ease of ultrasonic wave generation and the use of a piezoelectric vibrating element.
It is preferable to use ultrasonic waves having a frequency of about Hz.

[0039]

As described above, according to the present invention, ultrasonic waves are applied to the semiconductor film at the time of melting and recrystallization of the semiconductor film as a starting material, so that problems such as film roughness do not occur. A polycrystalline semiconductor film having an enlarged crystal grain size can be obtained.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing a method for manufacturing a polycrystalline semiconductor film according to an embodiment of the present invention.

2 is a timing chart showing the timing of laser irradiation and ultrasonic wave application in the embodiment of FIG.

3 is a diagram showing the relationship between the applied voltage to the piezoelectric vibrating element in the embodiment of FIG. 1 and the maximum crystal grain size of the obtained polycrystalline semiconductor film.

FIG. 4 is a diagram showing a method for manufacturing a polycrystalline semiconductor film according to another embodiment of the present invention.

5 is a diagram showing the relationship between the applied voltage to the piezoelectric vibration element and the maximum crystal grain size of the obtained polycrystalline semiconductor film in the example of FIG.

FIG. 6 is a diagram showing another example of an ultrasonic wave applying method.

[Explanation of symbols]

 1 Substrate 3 Semiconductor Film 5 Sample 6 Substrate Holder 7 Piezoelectric Vibrating Element 9 Laser Light 10 Light Source 11 Condensing Reflecting Mirror 12 Planar Reflecting Mirror 14 Antenna In the drawings, the same reference numerals indicate the same or corresponding parts.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 29/786 21/336

Claims (1)

[Claims] 1. A method for manufacturing a polycrystalline semiconductor film using a semiconductor film on a substrate as a starting material, wherein the semiconductor film is heated and melted while applying ultrasonic waves to the substrate or the semiconductor film, A method for producing a polycrystalline semiconductor film, which comprises forming the polycrystalline semiconductor film by crystallization.